I think I would plan on spending some weekends at shows in FL. There will be many horses there for sale, and you can also make contact with various trainers who may have other sale horses in their strings that are not showing.
Breeders are not usually likely to have FEI horses for sale, unless they also have a strong competition operation going on, and their own “in house” FEI rider. In general, that would usually be the larger operations like Hilltop, DG Bar, Iron Spring, etc.
If looking to import, I second Stafford Barton Stud. My trainer has been referring folks there for a couple of years. We also have contacts at various places in Germany - including places that supply some of the Stafford Barton horses. SBS tends to specialize in young horses, though, so is not likely to have FEI level horses.
In addition to our German contacts, we have some contacts in FL that have various FEI level horses for sale - some are fancier than others, but they are all sound, have good minds and rideability, and are reasonably priced.